The genome is the cardinal instrument of development that encodes the genetic parts and programs of an organism. With the sequencing of many genomes now complete, a next great frontier in the quest to understand the relationships between genotype and phenotype is to decipher how genome information is regulated. This frontier encompasses two essential attributes: regulatory code hardwired in genomes that specify spatial and temporal patterns of gene expression, and epigenetic influences that specify biological context to which a genome responds. This proposal investigates a complex odorant receptor (OR) gene regulatory system that is likely to reveal both novel genetic and epigenetic properties of the genome, and thus provide additional insights into how transcriptional regulation is coordinated genome-wide. Using cell lines derived from pre-neuronal progenitors, our experiments will provide insights into the deterministic and stochastic properties underlying mutually exclusive OR expression during the development of olfactory sensory neurons (OSNs). Specifically, we will characterize restricted OR expression potential in OSN progenitors, determine whether singular OR selection utilizes iterative regulatory mechanisms, elucidate epigenetic contributions to OR co-regulation, and investigate the biological significance of OR RNA nuclear localization. Broadly, these studies will contribute to our knowledge about the structural organization of genomes and the histone code as it pertains to gene co- regulation and cell differentiation. The development and characterization of an OSN cell culture system should have far-reaching utility to the neuroscience community, especially considering that olfactory neurons are one of the only known central neuron types in mammals that are capable of regeneration throughout the life of an organism. Research on epigenetic regulation also has far-reaching implications to the medical community, since imprinting-related diseases (e.g., Beckwith-Wiedemann syndrome), oncogenic transformation, and other genetic disorders (e.g., Thalassemia) are associated with perturbation of normal chromatin states. In total, this project will utilize and further develop a promising in vitro system for studying OR expression and OSN development, provide some of the first data on the OR epigenome, and contribute to our understanding of gene co-regulatory programs inherent in our genome.